You can choose between two sorting modes in Lambus:

In the automatic sorting mode, your stops will rearrange automatically when you add, change or delete a stop. The itinerary and your map change as well. This is useful if you already know where you will be.

In the manual sorting, stops remain in the order in which you added them. This is useful for sketching your trip together in the beginning. You can rearrange them by tapping "Edit" in your itinerary and then drag and drop the waypoints via the "☰" icon on the right.

Alternatively, you can tap on the stop number and enter the new number in the text field that pops up :).

You can easily switch between the sorting modes by going to your trip settings (the gear icon at the top right).

Then tap on Sort your stops to select between "By Date and "Manual"

To rearrange waypoints manually, see the following video for details: